1. Field of the Invention
The invention relates to (S)-hydroxynitrile lyases which have an altered substrate Acceptance.
2. Description of the Related Art
The implementation of chemical reactions with the aid of biological catalysts is gaining increasing importance, especially in those areas of application in which use can be made of the property, which is frequently pronounced in enzymes, are preferentially transforming one of the two enantiomers in reactions using chiral or prochiral components.
This group of enzymes includes the hydroxynitrile lyase (HNL) family, inter alia Hevea brasiliensis HNL (HbHNL) and Manihot esculenta HNL (MeHNL). The two enzymes exhibit a high sequence identity and belong to the proteins of the ".alpha./.beta.-hydrolase fold" type, which exhibit a characteristic tertiary fold and a so-called catalytic triad containing aspartic acid, serine and histidine as the active center. In this context, the active center is located at the inner end of a hydrophobic channel. In principle, HbHNL and MeHNL are suitable for converting a large number of carbonyl compounds, such as aliphatic, alicyclic, unsaturated, aromatic and heteroaromatic aldehydes and ketones, into the corresponding (S)-cyanohydrins. Since HNLs are gaining ever greater importance as biocatalysts for preparing (S)-cyanohydrins, attempts are constantly being made to improve their catalytic activity and substrate acceptance. The substrate acceptance of the HNLs which have so far been available is not satisfactory, particularly in the case of starting compounds possessing bulky residues, as a result of which the corresponding cyanohydrins are obtained either at a low conversion rate and/or in low enantiomeric excess.
The object of the invention was consequently to provide (S)-hydroxynitrile lyases having an improved substrate acceptance.